fix(javascript): transient Windows private-runtime source-transfer (#8769)

* fix(javascript): transient Windows private-runtime source-transfer

Parent source-transfer into the Windows private runtime root failed with
EPERM on path-based exclusive create. Write through a native transient
private-runtime path that closes the handle after flush so per-job rm
still works, and yield around the sync write so abort deadlines can fire.

* fix(javascript): yield timer phase before Windows source-transfer write

src/javascript/analysis/JavaScriptAnalysisSourceTransfer.ts

@@ -0,0 +1,45 @@
+import { writeFile } from "node:fs/promises";
+import { win32 } from "node:path";
+
+import { windowsPrivateRuntime } from "../../windows/WindowsPrivateRuntime.js";
+
+/**
+ * Parent source-transfer write into the worker-owned private runtime root.
+ *
+ * Windows private roots install a protected DACL and retain the directory
+ * handle; Node path-based exclusive create can fail with EPERM there. Write
+ * through the native private-runtime owner with a transient handle so the
+ * worker can `readFile` the path and the parent can still `rm` `${id}.source`
+ * after the job. POSIX keeps exclusive owner-only create.
+ */
+export const writeJavaScriptAnalysisSourceTransfer = async (
+  path: string,
+  source: string,
+  options: {
+    readonly platform?: NodeJS.Platform;
+    readonly signal?: AbortSignal;
+  } = {},
+): Promise<void> => {
+  const platform = options.platform ?? process.platform;
+  options.signal?.throwIfAborted();
+  if (platform === "win32") {
+    // Yield through a timer phase so ProviderStartupDeadline setTimeout
+    // callbacks and other macrotasks can deliver abort before the sync
+    // native create/write/flush/close; check again after it returns.
+    await new Promise<void>((resolve) => {
+      setTimeout(resolve, 0);
+    });
+    options.signal?.throwIfAborted();
+    windowsPrivateRuntime(win32.dirname(path)).writeTransientFile(
+      win32.basename(path),
+      source,
+    );
+    options.signal?.throwIfAborted();
+    return;
+  }
+  await writeFile(path, source, {
+    flag: "wx",
+    mode: 0o600,
+    signal: options.signal,
+  });
+};